1. Field of the Invention
The present invention is generally related to obturating bands of the type that are rotated at a rate independent of the rate of rotation of the projectile and, more particularly, to a method of manufacturing an obturating band whereby the free ends of a split ring pre-band which is placed in a projectile band seat are welded together to form a continuous single piece band.
2. Description of the Prior Art
Obturators for smart projectiles are most often of the despun type wherein only a portion of the rotational velocity imposed on the obturator by contact with the rifling in the gun barrel during firing is passed on to the projectile. An inner surface of the obturator fits against and rotates on a mating surface in the projectile sidewall or sabot sidewall. The mating surface is ordinarily a channel formed around the perimeter of the projectile or sabot. Obturators made from naturally slippery nylon or similar materials slip against the projectile body within the channel. Silicone oil or other friction reducing additive can be placed between the mating surface of the projectile and the inner surface of the obturator to enhance the slipping. The gun barrel rifling contacts an outer surface of the obturator and causes the obturator to rotate very quickly as it traverses the length of the gun. The projectile is caused to rotate at a speed less than would be achieved by a direct coupled obturator since despun obturators are permitted to slip within the projectile channel. However, a sufficient rotational velocity is imparted to offset any thrust vector misalignments.
U.S. Pat. No. 4,242,961 to Moredock et al discloses a chevron grooved decoupling obturator wherein the interior of the obturator ring is designed to slip rotationally with respect to the projectile body as the projectile travels along the barrel. The decoupling obturator minimizes the rotation of the projectile to one tenth the spin rate that would ensue if a suitable decoupling means were not provided. The obturator is made of 127E nylon which is naturally slippery and usually does not require a lubricant. However, Moredock et al do make provisions for the addition of a lubricant in the small clearance area inside the obturator ring. The obturator is slipped over a threaded portion at the aft end of the projectile and held in a channel by securing a threaded aft closure.
U.S. Pat. No. 4,552,071 to Horais et al discloses a two-piece despin obturator comprised of a ring shaped body made from nylon-6 and a wiper band made from Plascon nylon. The spiral lands of the gun barrel impart a high rotational velocity to the obturator. The rotational velocity is only partially coupled to the projectile through the friction of the inner surface of the nylon obturator on the steel obturator mount.
Neither Moredock et al nor Horais et al show a method for placing a despun obturator in a band seat which is of smaller diameter than adjacent sections of the projectile or sabot where the band seat and adjacent sections are integral. Moredock et al specifically show slipping the band on a surface of the projectile and then attaching a threaded member behind the band to create a non-integral channel. The preferred method to manufacture projectiles or sabot sections includes forming an integral band seat in the form of a channel about the projectile or sabot perimeter. Forming an integral band seat channel requires less process steps than forming two pieces which are mated by a threaded section.
The prior art shows projectiles with obturating bands that have been assembled in an integral band seat channel of the projectile or sabot. U.S. Pat. No. 4,446,795 to Price et al and U.S. Pat. No. 4,381,319 to Hargeaves et al disclose processes in which the band seat zone is sprayed with a metallic coating and a polymer is molded over the sprayed metallic coating to form a plastic rotating band. U.S. Pat. No. 4,558,646 to Hoffmann et al discloses a projectile body with a rotating plastic band where the band is injection molded directly in the groove around the projectile diameter. U.S. Pat. No. 3,910,194 to Dehm et al discloses chemically bonding a rotating band by applying molten plastic to a heated projectile and then cooling the projectile.
None of the patents described above, wherein the rotating band is formed within the band seat channel by molding techniques, disclose a despun obturator as an end product. All of the patents form an obturating band which is bonded by some means to the projectile body. Hence, the obturating bands formed in the above-identified patents are directly coupled to the projectile and all of the spin imparted from the gun barrel rifling to the obturating band will therefore be transferred to the projectile body.
U.S. Pat. No. 4,532,868 to Gleichaut et al discloses a obturating band for projectiles that is positioned in an integral groove in the projectile and is held in place by a latching connection. The latch may have a dovetail or hook configuration which effectively prevents bursting open of the band under centrifugal force. However, this design prevents slippage between a rotating band and the body of the projectile as .well. Moreover, the resulting obturating band is not one continuous ring. The latch portion will have different properties from the rest of the band.
There is no teaching in the prior art of a obturating band in a band seat channel integrally formed about the perimeter of a projectile or sabot. There is no teaching in the prior art of a means for forming an obturating band starting with a split ring pre-band and forming a continuous ring using ultrasonic welding or heat staking technology wherein the resulting obturating band is of the despun variety and is formed within a band seat channel about the perimeter of a projectile or sabot.